In the aviation industry, large commercial jetliners in the air transport market typically have both autopilot and autothrottle systems thereon to aid a pilot in controlling the speed and attitude of the aircraft. In smaller, general aviation aircraft, such as business jets and commuter planes, typically there is no autothrottle system. The pilot is left with the task of manually making all throttle or thrust adjustments. However, general aviation autopilots have typically used elevator adjustments, commanded by the autopilot, to control airspeed. While this approach has been used widely in the past, it does have some drawbacks when the pilot induced throttle changes oppose the autopilot elevator control.
When a pilot selects a higher desired airspeed the autopilot may pitch the aircraft down to gain more speed. If the pilot increases the throttle setting to attain the higher airspeed and causes a rate-of-change of airspeed which exceeds the rate limit set by the autopilot, the autopilot may command a pitch-up to reduce the rate-of-change of airspeed. The result is that the aircraft makes large undesirable pitch attitude excursions and takes longer to reach the desired airspeed. A similar problem exists when a pilot wishes to simultaneously descend and reduce airspeed, and reduce thrust.
Consequently, there exists a need for improved autopilot systems which do not exhibit the undesirable pitch attitude excursions.